Occupational Safety in Uranium Mining

There has been more than 40 years of experience in applying international radiation safety regulations at uranium mines.

Australian and Canadian radiation safety regulations today are among the most comprehensive and stringent in the world.

Radiation doses at Australian and Canadian uranium mines are well within regulatory limits.

Uranium mining companies have generally taken active steps to reduce radiation doses wherever and whenever they can, and voluntarily adopted the most recent international recommendations on dose limits long before they became part of the regulations.

All of us receive a small amount of radiation all the time from natural sources such as cosmic radiation, rocks, soil and air. Uranium mining does not increase this discernibly for members of the public, for aboriginal people living near the mines, or for others outside the industry.

For people involved in mining there is potential exposure to what are in fact naturally-occurring radioactive materials (NORM). As for other occupational health hazards, monitoring and then controlling the risks is necessary.

A dose is the amount of medically significant radiation a person receives.

In Australia, mining operations are undertaken under the country's Code of Practice and Safety Guide for Radiation Protection and Radioactive Waste Management in Mining and Mineral Processing, administered by state governments (and applying also to mineral sands operations). In Canada, the Canadian Nuclear Safety Commission regulations apply. In other countries there are similar arrangements to set health standards for gamma radiation and radon gas exposure, as well as for ingestion and inhalation of radioactive materials. Standards apply to both workers' and public health.

The product of uranium mining is normally uranium oxide concentrate – U3O8 – which is shipped from the mines in 200-litre drums. This is barely radioactive, but has chemical toxicity similar to lead, so occupational hygiene precautions are taken similar to those in a lead smelter. Most of the radioactivity from the ore ends up in the tailings.

The basis of radiation protection standards

In practice, radiation protection is based on the understanding that small increases over natural levels of exposure are not likely to be harmful but should be kept to a minimum. To put this into practice the International Commission for Radiological Protection (ICRP) has established recommended standards of protection (both for members of the public and radiation workers) based on three basic principles:

Justification. No practice involving exposure to radiation should be adopted unless it produces a net benefit to those exposed or to society generally.

Optimisation. Radiation doses and risks should be kept as low as reasonably achievable (ALARA), economic and social factors being taken into account.

Limitation. The exposure of individuals should be subject to dose or risk limits above which the radiation risk would be deemed unacceptable.

These principles apply to the potential for accidental exposures as well as predictable normal exposures.

Underlying these is the application of the "linear hypothesis" based on the idea that any level of radiation dose, no matter how low, involves the possibility of risk to human health. This assumption enables "risk factors" derived from studies of high radiation dose to populations (eg from Japanese bomb survivors) to be used in determining the risk to an individual from low doses (ICRP Publication 60). However the weight of scientific evidence does not indicate any cancer risk or immediate effects at doses below ablout 50 millisievert (mSv) per year.

Based on these conservative principles, ICRP recommends that the additional dose above natural background and excluding medical exposure should be limited to prescribed levels. These are: one millisievert per year for members of the public, and 20 mSv per year averaged over 5 years for radiation workers who are required to work under closely-monitored conditions.

The frameworks of radiation safety in countries where most uranium is mined are based on the full adoption of international recommendations. This is not the case in all parts of the world. Even the 1977 Recommendation of the ICRP has not been universally adopted.

The safety record of the uranium mining industry is good. Radiation dose records compiled by mining companies under the scrutiny of regulatory authorities have shown consistently that mining company employees are not exposed to radiation doses in excess of the limits. The maximum dose received is about half of the 20 mSv/yr limit and the average is about one tenth of it. (This compares with natural doses of up to 50 mSv/yr for some places in India and Europe, without any adverse effects being evident, and mean exposures of 750 mSv/yr in some East German mines from 1946 to 1954, resulting in thousands of cases of lung cancer.)

Furthermore, doses are reduced by programs of education and training, as well as engineering design.

Achieving effective radiation safety

Although uranium itself is barely radioactive, the ore which is mined must be regarded as potentially hazardous due to uranium’s decay products, especially if it is high-grade ore. The gamma radiation comes principally from isotopes of bismuth and lead in the uranium decay series. The radiation hazards involved are similar to those in many mineral sands mining and treatment operations.

Radon gas emanates from the rock (or tailings) as radium decays. It then decays itself to (solid) radon daughters, which are energetic alpha-emitters. Radon occurs in most rocks and traces of it are in the air we all breathe. However, at high concentrations it is a health hazard since its short half-life means that disintegrations giving off alpha particles are occurring relatively frequently. Alpha particles discharged in the lung can later give rise to lung cancer.

A number of precautions are taken at a uranium mine to protect the health of workers:

Dust is controlled, so as to minimise inhalation of gamma- or alpha-emitting minerals. In practice dust is the main source of radiation exposure in an open cut uranium mine and in the mill area.

Radiation exposure of workers in the mine, plant and tailings areas is limited. In practice radiation levels from the ore and tailings are usually very low. At Olympic Dam, direct gamma exposure comprises about half the miners' dose and for those in the mill, a quarter.

Radon daughter exposure is kept low. It is minimal in an open cut mine because there is sufficient natural ventilation to remove the radon gas. At Ranger the radon level seldom exceeds one percent of the levels allowable for continuous occupational exposure. In an underground mine a good forced-ventilation system is required to achieve the same result – at Olympic Dam radiation doses in the mine from radon daughters are kept very low, with an average of less than about 1mSv/yr. Canadian doses (in mines with high-grade ore) average about 3 mSv/yr.

Strict hygiene standards are imposed on workers handling the uranium oxide concentrate. If it is ingested it has a chemical toxicity similar to that of lead oxide (Both lead and uranium are toxic and affect the kidney. The body progressively eliminates most Pb or U, via the urine). In effect, the same precautions are taken as in a lead smelter, with use of respiratory protection in particular areas identified by air monitoring.

These precautions with respect to radon are a relatively new phenomenon. From the fifteenth century, many miners who had worked underground in the mountains near the present border between Germany and the Czech Republic contracted a mysterious illness, and many died prematurely. In the late 1800s the illness was diagnosed as lung cancer, but it was not until 1921 that radon gas was suggested as the possible cause. Although this was confirmed by 1939, between 1946 and 1959 a lot of underground uranium mining took place in the USA without the precautions which might have become established as a result of the European experience. In the early 1960s a higher than expected incidence of lung cancer began to show up among miners who smoked. The cause was then recognized as the emission of alpha particles from radon and, more importantly, its solid daughter products of radioactive decay. The miners concerned had been exposed to high levels of radon 10-15 years earlier, accumulating radiation doses well in excess of present recommended levels.

The small, unventilated uranium "gouging" operations in the USA which led to the greatest health risk are a thing of the past. In the last 50 years, individual mining operations have been larger, and efficient ventilation and other precautions now protect underground miners from these hazards. Open cut mining of uranium virtually eliminates the danger. There has been no known case of illness caused by radiation among uranium miners in Australia or Canada. While this may be partly due to the lack of detailed information on occupational health from operations in the 1950s, it is clear that no major occupational health effects have been experienced in either country.

While uranium oxide product from a mine is certainly radioactive, the long half-lives involved mean that it is practically impossible to receive a harmful radiation dose from it. Cameco points out that for a person standing one metre from a 200-litre drum of product they would need to be there about one thousand hours to register a dose of 1 mSv. Uranium ore and mine tailings are more radioactive, depending on the grade of the orebody, but usually not to such a degree that access needs to be restricted.

Radiation safety regulation in Australia

When the current era of uranium mining began in Australia in the 1970s, a review of the regulatory framework for radiation safety was undertaken. This resulted in the production of the 1975 Commonwealth Code of Practice on Radiation Protection in the Mining and Milling of Radioactive Ores (the 'Health Code'). The Health Code was formulated from recommendations made by the International Commission on Radiological Protection (ICRP) and the radiation dose limits adopted by the National Health and Medical Research Council (NHMRC). It was revised in 1980 and again in 1987.

This Health Code had legal force in the States and Territories only when it was adopted under State and Territory Acts or Regulations.

In the Northern Territory (where the Ranger uranium mine is located), the Health Code was adopted as a Condition of Licence under the Mining Act Regulations, thus giving it legal status.

In South Australia the Health Code was given legal status initially through the Act setting up the Olympic Dam mine.

In addition to the Health Code there was the Code of Practice on the Management of Radioactive Wastes from the Mining and Milling of Radioactive Ores (1982) – the 'Waste Code' – which was given legal force in the States and Territories in much the same way as the Health Code, i.e. imposed as Condition of Licence under State and Territory Acts.

Responsibilities for administration of the Health Code are divided between the Health Department and the Mines Department or their equivalent bodies in the States and Territories. The Health Department is responsible for ensuring that the basic radiation exposure standards are complied with, while the Mines Department is responsible for the day-to-day overseeing of the general occupational health and safety requirements at mine sites.

The Code and Guide is complemented by the Radiation Workers' Handbook, developed by industry and government in collaboration. This can be downloaded from the Minerals Council of Australia website.

In addition there is the Code of Practice for the Safe Transport of Radioactive Substances (1990), also given legal force in the States and Territories in much the same way as the other code.

Radiation protection standards

Following the ICRP-60 recommendations published in 1991, the NHMRC and the National Health & Safety Commission jointly prepared new Australian Recommendations for limiting exposure to ionising radiation and a National Standard for limiting occupational exposure. These are consistent with the Basic Safety Standards for radiation protection adopted in 1994 by various UN agencies.

The revised occupational exposure limit is 20 millisieverts per year averaged over five consecutive years. (Exposure limits for members of the public from radiation-related activities remained at 1 mSv per year, which is less than the average radiation background from the environment.) These NHMRC recommendations were incorporated in the revised code in 2005.

Since the early 1990s, all mining companies have voluntarily agreed to adopt the ICRP-60 Recommendations, without waiting for the complete revision of the Health Code which emerged in 2005.

Appendix:

Radon and radon progeny

The concentration of radon decay progeny (RnDP) is measured in Working Levels or in microjoules of ultimately-delivered alpha energy per cubic metre of air. One 'Working Level' (WL) is approximately equivalent to 3700 Bq/m3 of Rn-222 in equilibrium with its decay progeny (the main two of which are the very short-lived alpha-emitters), or to 20.7 μJ/m3. The former assumes still air, not proper ventilation. One working level month (WLM) is the dose from breathing one WL for 170 hours, and the former occupational exposure limit was 4 WLM/yr. It was generally taken that 4 WLM is epidemiologically equivalent to 20 mSv, the average occupational dose limit. Today the ICRP recommended limit is 3.5 μJ/m3, which is a measure of the actual RnDP situation in whatever conditions of ventilation prevail. It is generally equivalent to about 2000 hours per year exposure to 3000 Bq/m3 of radon in a ventilated mine where the radon is removed and so is not in equilibrium with its decay progeny.

A background radon level of 40 Bq/m3 indoors and 6 Bq/m3 outdoors, assuming an indoor occupancy of 80%, is equivalent to a dose rate of 1 mSv/yr and is the average for most of the world's inhabitants. Exposure levels of less than 200 Bq/m3 (and arguably much more) are not considered hazardous unless public health concerns are based on LNT assumptions.